Middle East Respiratory Syndrome (MERS) coronavirus (MERS-CoV) causes severe acute respiratory illness with a high fatality rate among reported cases. MERS was first reported in 2012, but the virus has been circulating in camels, which are thought to be an animal reservoir, for at least 20 years. To date over 1000 MERS cases have been reported to the World Health Organization, including over 400 deaths. While most cases have been in Saudi Arabia and contact with camels or camel products has been implicated in some cases, human-to-human transmission has been documented as well and the virus is thought to have epidemic potential. There are currently no approved vaccines or therapeutics for MERS. The MERS-CoV spike (S) protein mediates viral entry into host cells expressing the viral receptor dipeptidyl peptidase 4 (DPP4). Within the S1 subunit, a Receptor Binding Domain (RBD) of about 200 amino acids has been identified. Immunization of mice with a recombinant fusion protein containing S377-588 fused to human IgG1 Fc (S377-588-Fc) induced high titers of neutralizing antibodies in immunized animals. Unfortunately, expression of S377-588-Fc (or RBD-Fc) in mammalian cell culture is low, which may be an impediment for further development of this promising candidate vaccine. We will circumvent the production problem by producing MERS-CoV RBD-Fc, and modifications thereof, using a well-established plant-expression system. Our scalable transient plant-expression system allows rapid production of recombinant protein (within a week); with protein production costs less than 10% that of mammalian cell systems. We will produce variants of MERS-CoV RBD-Fc with enhanced binding to the mouse neonatal Fc receptor (FcRn), in order to test the hypothesis that improved antigen presentation via FcRn will result in an enhanced immune response. We will evaluate the immunogenicity of mucosally-administered MERS-CoV RBD-Fc in mice, by analyzing both humoral and cell-mediated immunity. We will evaluate titers of RBD-specific antibodies, analyze T cell responses by intracellular cytokine staining followed by flow cytometry analysis, and will measure the ability of sera from immunized mice to neutralize live MERS-CoV in vitro.